1. Field of the Invention
The present invention relates to a phosphatidylinositol 3-kinase activity regulator including the fifth zinc finger domain of FOG2.
2. Description of the Related Art
The Phosphatidylinositol 3-kinase (PI3K) which consists of p110 catalytic subunit and p85α regulatory subunit is a heterodimeric protein and activated by receptor tyrosine kinase (RTK) growth factors. The p85α regulatory subunit comprises multiple domains including two SH2 domains that are separated by inter-SH2(iSH2), which binds to p110 catalytic subunit. iSH2 domains that are required to bind to p110 consist of coiled-coil regions.
PI3K is a main downstream effector of receptor tyrosine kinases (RTK) and G protein-coupled receptors (GPCRs), mediates various intracellular signal transduction using phosphatidylinositol-3,4,5-triphosphates (PIP3), which is generated by phosphorylating PIP2. The downstream signal transduction of PI3K includes such as, RAC1, SGK, PKC, Akt, MDM2, FOXO1, NFκB, BAD, GSK3β and mTOR. The upstream signal transduction affected to PI3K activity includes PTEN, which is known to inhibit the RTK and PI3K activities regulated by insulin and growth factors.
Akt signal transduction is involved in the cell growth through NF-κB and Bcl2 consisting of the downstream signal transduction of Akt phosphorylated by PIP3. Akt signal transduction regulates the cell proliferation and death via controlling apoptosis by Fas (Trotman L C et al, Cancer Cell, 2003, 3:97-99) and also regulates cell cycles via p27 and glycogen synthase kinase 3 (GSK3) (Kiyokawa H et al, Cell, 1996, 85: 721-732; Hsieh F F et al, Blood, 2000, 96:2746-2754; Sears R et al., Genes Dev, 2000, 14: 2501-2514). Furthermore, Akt signal transduction increases the protein synthesis and the cell growth (cell size) by mTOR (mammalian target-of-rapamycin) and plays an important role in cell growth (Wullschleger S et al., Cell, 2006, 25:6423-6435).
As described above, PI3K is involved in various intracellular reactions and has been studied as a target of the disease which is caused by a abnormal signal transduction. Recently, it has been reported that the role of PI3K in autoimmune diseases including PI3K, systemic lupus erythematosus and rheumatoid arthritis; respiratory diseases including allergic asthma and chronic obstructive pulmonary disease; and cardiovascular disorders including atherosclerosis and myocardial infarction (Ghigo A et al., Bioessays, 2010, 32(3):185-96), and also reported the relation of intracellular insulin signal transduction and PI3K signal transduction (W. El Kholy et al., FASEB J. 2003, 17, 720-722).
In connection with cancers, PI3K regulates the cell growth and cell death and it has been targeted in cancer treatment researches via regulating the cancer cell proliferation, growth and cell death. PI3K performs an important role that regulates the cell motility in tumor metastasis. PI3K regulates cell motilities by enabling the cell migration and invasiveness and also regulates cell mobilities by controlling the actin dynamics through the interaction of p85α, small GTPase Rac and Cdc42. In addition, p85α subunit increases PI3K activity by interacting with intracellular proteins such as protein kinase C, SHP1, Rac, Rho, hormonal receptors, Ras and Src. Namely, increasing the cancer metastasis and cancer cell motility, PI3K activity is increased. Similarly, it has been reported the research of cancer treatments by using PI3K-pan inhibitors, specific PI3K isoform inhibitors or flavonoids (Hou D X, et al., Antiosid Redox Signal, 2010).
Additionally, in a metabolic disease, it has been demonstrated that p110 catalytic subunit of PI3K is an important role in metabolic regulation (Lazaros. C., et al, Nature letters, 2006). Accordingly, the abnormal signal transduction through the insulin receptor substrate (IRS) protein was shown in knock-out mice having the heterozygosity form (universally expressed) of p110 catalytic subunit. IRS is an important protein mediating the signal transduction of insulin-like growth factor 1 and leptin. Reacting with these hormones defectively, it was shown the somatic cell growth, hyperinsulinemia, glucose tolerance, hyperphagia and lipids increase.
In a cardiac disease, it has been reported that PI3K-PTEN signal transduction regulates the heart contractility and cardiac cell size (Michael A. et al., Cell, 2002). Accordingly, PI3K-PTEN signal transduction regulated various intracellular reactions and inactive PTEN, a tumor suppressor, reduced the heart contractility in myocardiocyteal muscle cells and caused a cardiomegaly. In other studies, it has been known that Class IA PI3K controlled the heart size and related with the cardiomegaly (Ji Luo et al, Molecular and Cellular Biology, 2005). The cardiomegaly was shown by overexpressing p110α of PI3K subunit, however, the heart was contracted by overexpressing the dominant negative p110α (Shioni, T., et al, EMBO, 2000).
Similarly the role of PI3K regulating the somatic cell proliferation, PI3K increased a stem cell proliferation in gain of function models which was increased PI(3,4,5)P3. Based on these results that PI3K inhibitor reduced the cell proliferation, it has been reported that PI3K facilitated the stem cell proliferation (Takahashi K et al., Biochem Soc. Trans. 2005, Vanhaesebroeck B. et al., Trends Biochem., 2005). However, it has been shown that the stem cell differentiation was promoted by PI3K inhibition and PI3K played an important role in retaining the pluripotency (Amstrong, L et al, Hum. Mol. Genet, 2006, Pyle, A. D. et al., Nat. Biotech., 2006, M. J Wellham et al., Biochem. Soc. Trans, 2007).
FOG2 (Friend of GATA 2) is one of transcriptional complement factors which is known to regulate GATA activity by binding to GATA transcription factors. FOG2 comprises eight zinc fingers including 4 C2H2-type and 4 C2H2-type zinc fingers. Recently, it has been reported that FOG2 can be regulated by miR-130 α in heart development. In our previous study, miR-200 family regulates a metabolic process such as the cell proliferation and survival by targeting FOG2 (S. Hyun., et al., Cell, 2009). Because these results are shown in a fly and human cells, it can be highly possible to conserve these processes evolutionarily. In mammal cell systems, FOG2, a negative regulator, directly bind to p85α and interferes with PI3K heterodimer complex (S. Hyun., et al., Cell, 2009).
Cys2His2 zinc-fingers (C2H2 zinc finger) of FOG2 protein mediate various bindings between protein-DNA or protein-protein. The zinc finger domain which has small size and self-folding protein structures, regulates interactions of zinc ions generally conserved in cysteine or histidine amino acids residues. These motifs forms ββα structures and are stabilized by combining zinc ions. However, there has been no report that FOG2 and its zinc finger domain have the anti-cancer activity.
Here, we investigate the PI3K activity which involves various intracellular mechanisms, and find out that the fifth zinc finger domain of FOG2 regulates PI3K/Akt activity, cancer cell migration and the reduction of cell survival.